Contact devices are used for electromagnetic relays and the like, and a contact device used for an electromagnetic relay is described in JP 2011-23332A. This contact device includes a fixed terminal that has a pair of fixed contacts, a movable contact plate that has a pair of movable contacts and moves toward and away from the fixed terminal, a drive portion configured to move the movable contact plate toward the fixed terminal, a pressing spring that biases the movable contact plate toward the fixed contact, and a case that accommodates these components.
The drive portion includes a shaft that is inserted into the movable contact plate, and a first yoke plate that is provided at one end of the shaft and restricts the movement of the movable contact plate toward the fixed terminal. Meanwhile, a second yoke plate is fixed to the movable contact plate on the opposite side to the movable contacts.
In the contact device, when the shaft moves toward the fixed terminal by the drive of the drive portion, the first yoke plate also moves in the same direction. Therefore, in this case, the movable contact plate moves toward the fixed terminal by the biasing force of the pressing spring, and the movable contacts come into contact with the fixed contacts to allow current to flow. By the flow of current, a magnetic field is generated around the movable contact plate, and a magnetic attractive force is generated between the first yoke plate and the second yoke plate. Since the magnetic attractive force cancels out the repulsive force generated at the contacted region between the contacts, the reduction of the pressing force between the contacts can be mitigated and the movable contacts can be favorably brought into contact with the fixed contacts.
The contact device described above is structured such that the movable contacts that are brought into contact with the fixed contacts are provided as a pair, and the movable contacts are brought into contact with respective fixed contacts by the biasing force of the pressing spring. However, in such a structure in which the movable contacts are provided as a pair, the contact of the movable contacts to the fixed contacts becomes unstable due to the vibration of the movable contact plate under the action of an electromagnetic force caused by the current or external vibration.
Thus, a structure is conceivable in which a movable contact plate is provided with three movable contacts, and the movable contact plate is brought into contact with fixed contacts at three regions. However, in the case where the movable contact plate is brought into contact with the fixed contacts at three regions, there is a problem in that when an acting force on the movable contact plate is localized, it becomes difficult to bring all of the three movable contacts stably into contact at the three regions, and current does not flow stably.